Deck 17: Three-Phase Motors

Question 1

It is possible to determine the direction of rotation of a motor before power is connected to it with the use of a ____ meter.

A) rotation direction
B) phase
C) motodirection
D) phase rotation

Answer 1

D

Question 2

The amount of torque produced by an AC induction motor is determined by three factors: strength of the magnetic field of the stator, strength of the magnetic field of the rotor, and phase angle difference between rotor and stator fields.

Answer 2

True

Question 3

A squirrel-cage rotor is made by connecting wires to two end rings.

Answer 3

False

Question 4

Consequent pole squirrel-cage motors permit the synchronous speed to be changed by changing the number of stator poles.

Question 5

The wound-rotor induction motor was very popular in industry for many years because of its low starting torque and high starting current.

Question 6

Selsyn motors are used to provide position control and angular feedback information in industrial applications. The word selsyn is a contraction derived from ____.

A) selected synchronization
B) selected synthetic
C) self-synchronous
D) self-synthetic

Question 7

Selsyn motors never operate as transformers.

Question 8

When a motor is to be connected for low-voltage operation, the phase windings must not connect in parallel.

Question 9

The rotor of a synchronous motor contains a set of squirrel-cage bars similar to those found in a type A rotor. This set of squirrel-cage bars is used to start the motor and is known as the ____ winding.

A) asynchronous
B) field resistor
C) electromagnetic
D) amortisseur

Question 10

The line current supplying a squirrel-cage motor can be computed using the formula: I(LINE) = VA / (E(LINE) x ____)

A) 1.543
B) 1.732
C) 2.4
D) 5

Question 11

What is the synchronous speed of a four-pole motor connected to 50 Hz?

A) S = 1.67 RPM
B) S = 9.6 RPM
C) S = 1500 RPM
D) S = 6000 RPM

Question 12

All three basic types of three-phase motors operate on the same principle, and they all use the same basic design for the stator windings.

Question 13

The DC power of a synchronous motor can be provided by several methods. The most common of these methods is either a small DC generator mounted to the shaft of the motor or an electronic power supply that converts the AC line voltage into DC voltage.

Question 14

Consequent pole motors that are intended to operate with three speeds contain ____ separate stator windings.

A) two
B) three
C) three or four
D) four

Question 15

The pull-out torque for most synchronous motors will range from ____ of rated full-load torque.

A) 50% to 75%
B) 100% to 150%
C) 125% to 175%
D) 150% to 200%

Question 16

The advantage of using a synchronous condenser over a bank of capacitors for power factor correction is that the amount of correction is easily controlled.

Question 17

A rotor slip of 14% to 17% is common for most squirrel-cage induction motors.

Question 18

The rotor of a wound rotor motor is constructed by winding three separate coils on the rotor ___ degrees apart.

A) 45
B) 90
C) 120
D) 180

Question 19

The ____ selsyn is used to produce the algebraic sum of the rotation of two other selsyn units.

A) sequential
B) differential
C) synchronous
D) rotational

Question 20

The squirrel-cage motor is an induction motor, which means that the current flow in the rotor is produced by ____ voltage from the rotating magnetic field of the stator.

A) induced
B) reduced
C) increased
D) spikes in